'\" e
'\"! eqn | mmdoc
'\"macro stdmacro
.ds Vn Version 1.2
.ds Dt 24 September 1999
.ds Re Release 1.2.1
.ds Dp Jan 14 18:30
.ds Dm 01 clipplane
.ds Xs 34226 5 clipplane.gl
.TH GLCLIPPLANE 3G
.SH NAME
.B "glClipPlane
\- specify a plane against which all geometry is clipped

.SH C SPECIFICATION
void \f3glClipPlane\fP(
GLenum \fIplane\fP,
.nf
.ta \w'\f3void \fPglClipPlane( 'u
	const GLdouble \fI*equation\fP )
.fi

.EQ
delim $$
.EN
.SH PARAMETERS
.TP \w'\fIequation\fP\ \ 'u 
\f2plane\fP
Specifies which clipping plane is being positioned.
Symbolic names of the form \%\f3GL_CLIP_PLANE\fP\f2i\fP,
where \f2i\fP is an integer between 0 and \%\f3GL_MAX_CLIP_PLANES\fP$^-^1$,
are accepted.
.TP
\f2equation\fP
Specifies the address of an array of four double-precision floating-point values.
These values are interpreted as a plane equation.
.SH DESCRIPTION
Geometry is always clipped against the boundaries of a six-plane frustum
in \f2x\fP, \f2y\fP, and \f2z\fP.  
\%\f3glClipPlane\fP allows the specification of additional planes,
not necessarily perpendicular to the \f2x\fP, \f2y\fP, or \f2z\fP axis,
against which all geometry is clipped.
To determine the maximum number of additional clipping planes, call
\%\f3glGetIntegerv\fP with argument \%\f3GL_MAX_CLIP_PLANES\fP. All
implementations support at least six such clipping planes. 
Because the resulting clipping region is the intersection
of the defined half-spaces,
it is always convex.
.P
\%\f3glClipPlane\fP specifies a half-space using a four-component plane equation.
When \%\f3glClipPlane\fP is called,
\f2equation\fP is transformed by the inverse of the modelview matrix
and stored in the resulting eye coordinates.
Subsequent changes to the modelview matrix have no effect on the
stored plane-equation components.
If the dot product of the eye coordinates of a vertex with the
stored plane equation components is positive or zero,
the vertex is \f2in\f1 with respect to that clipping plane.
Otherwise, it is \f2out\fP.
.P 
To enable and disable clipping planes, call
\%\f3glEnable\fP and \%\f3glDisable\fP with the argument 
\%\f3GL_CLIP_PLANE\fP\f2i\fP, 
where \f2i\fP is the plane number.
.P
All clipping planes are initially defined as (0, 0, 0, 0) in eye coordinates
and are disabled.
.SH NOTES
It is always the case that \%\f3GL_CLIP_PLANE\fP$i$ = \%\f3GL_CLIP_PLANE0\fP$~+~i$.
.SH ERRORS
\%\f3GL_INVALID_ENUM\fP is generated if \f2plane\fP is not an accepted value.
.P
\%\f3GL_INVALID_OPERATION\fP is generated if \%\f3glClipPlane\fP
is executed between the execution of \%\f3glBegin\fP
and the corresponding execution of \%\f3glEnd\fP.
.SH ASSOCIATED GETS
\%\f3glGetClipPlane\fP
.br
\%\f3glIsEnabled\fP with argument \%\f3GL_CLIP_PLANE\fP\f2i\fP
.SH SEE ALSO
\%\f3glEnable(3G)\fP
